This volume outlines the development, testing and use of German railroad guns, although information on actual employment is rather limited. While the other does list the various German railroad artillery regiments and batteries, the OB is incomplete and confusing. Basic technical data on each German-made weapon is listed, but not for the French weapons (although figures for range are usually given in photo captions). While certainly only an introduction to this subject, this volume does succeed in providing a handy and inexpensive reference to a relatively obscure subject.